The IEEE (The Institute of Electrical and Electronics Engineers Inc.) has set forth IEEE 802.11ac, which realizes even higher speeds than IEEE 802.11 that is a wireless LAN (Local Area Network) standard. The IEEE currently has started work on standardization of IEEE 802.11ax as a successor standard for IEEE 802.11ac. Improved throughput per user in an environment where wireless LAN devices are overcrowded is being studied in standardization of IEEE 802.11ax as well, to handle the rapid increase of wireless LAN devices.
A wireless LAN system is a system where each wireless LAN device secures its own resources in an autonomous decentralized manner (autonomous decentralized system). An autonomous decentralized system is a system in which temporal synchronization among wireless LAN devices, and exchange of complicated control information, are not required. Accordingly, a wireless network can be configured using wireless LAN devices that have a relatively simple configuration. Autonomous decentralized systems are well-suited for unlicensed band, due to the ease of configuring wireless networks.
Usage situations of wireless LAN systems have become markedly diversified due to the rapid spread thereof in recent years. For example, situations such as a wireless carrier using a wireless LAN system for offloading wireless mobile communication traffic, providing public wireless LANs primarily targeting foreign tourists, and so forth, have already been realized, with wireless LAN base stations (AP: Access Point) being installed in train stations, large-scale commercial facilities, and so forth. Thus, wireless LANs have been actively installed in locations where people congregate, with Internet services being actively provided.
The standardization of IEEE 802.11ax aims to improve throughput in environments where wireless LAN devices are overcrowded, viewed against the background of diversity in usage situations of wireless LAN, and technology for introduction thereof is being studied.
One technology being studied for standardization of IEEE 802.11ax is uplink multiple access technology. Uplink multiple access technology is technology where multiple LAN device perform transmission collaboratively, temporal synchronization among wireless LAN devices and exchange of control information being required of the wireless LAN devices. Accordingly, detailed discussion is being held in standardization of IEEE 802.11ax, with regard to temporal synchronization of wireless LAN devices and procedures for exchange of control information.
NPL 1 proposes procedures for uplink MU-MIMO. According to NPL 1, a wireless LAN base station transmits a frame that triggers initiation of uplink MU-MIMO (trigger frame). An arrangement is used where a wireless LAN device that has received the trigger frame initiates transfer of data at a predetermined point in time, if participation in the uplink MU-MIMO has been instructed by the wireless LAN base station, thereby easily enabling temporal synchronization among wireless LAN devices.